食品辐照技术中使用的丙氨酸-ESR剂量测量方法的研究-ESR测量条件的选定

鉴于丙氨酸辐照后形成的自由基很稳定,其总数在食品辐照常用的剂量范围(10²~10⁴Gy)内正比于辐照剂量,我们选定丙氨酸-ESR系统作为我国γ射线大剂量传递剂量计,并对它进行了研究,确定了正常的ESR测量条件。特别修正了波谱仪的增益系数之间的线性关系并计测了旋转样品管对信号幅度的影响。检测吸收剂量的下限为5Gy。在0.05~1k7Gy的范围内,对于以十种不同剂量辐照的丙氨酸样品,ESR波谱主峰幅度h与相应的剂量D之间的线性相关系数大于0.999。     

沉积物中石英ESR测年功率饱和效应的初步研究

介绍了几组沉积物中石英ESR功率饱和效应的基础实验情况,认为在用石英进行ESR测年时,微波功率的选择是一个重要参数,它直接影响累积剂量(AD)的求取,从而严重影响测年结果。在某些特定的地质环境下(如黄土,海洋沉积物),采用比较高的微波功率,可从沉积物石英的E＇心得到较老沉积物(大于50万年)可信的ESR年代。     

沉积物中石英ESR测年功率饱和效应的初步研究

介绍了几组沉积物中石英ESR功率饱和效应的基础实验情况,认为在用石英进行ESR测年时,微波功率的选择是一个重要参数,它直接影响累积剂量(AD)的求取,从而严重影响测年结果。在某些特定的地质环境下(如黄土,海洋沉积物),采用比较高的微波功率,可从沉积物石英的E'心得到较老沉积物(大于50万年)可信的ESR年代。     

运用ESR方法测定一些地质样品年龄的尝试

本文介绍了用ESR测地质年代方法的发展、现状及基本原理。给出了用ESR方法测定四川鲜水河地震活动断裂带的泉华样品、泥河湾的丽蚌化石样品、北京周口店洞穴中石笋样品的天然辐射总剂量AD的初步结果。测定周口店洞穴中石笋样品的年龄为(6×10⁴)年。并对结果进行了讨论。最后,还就有关ESR测年代方法的一些有关问题进行了探讨。     

细胞松弛素B阻断微核法鉴定男性个体辐射敏感性的方法初探

初步研究了男性个体辐射敏感性的鉴定方法及标准.采集50名男性志愿者的外周血,分别给予不同剂量X射线照射,采用细胞松弛素B阻断双核法测定微核率(MNF),通过二阶多项拟合法,绘制微核剂量效应选项中心标准曲线,将个人微核剂量效应曲线与标准曲线比对后判断个体辐射敏感性.0.0～2.5 Gy剂量范围内,剂量效应二阶多项拟合的中...     

剂量引导精确放射治疗中三维评价算法设计及实现

针对临床剂量学验证中二维评价方法只能反映每张平片上剂量分布情况, 并根据剂量引导精确放疗系统中三维剂量验证需求设计算法实现对三维剂量分布的比较。 根据公式, 在Visual C++控制台下实现剂量偏差、 位置偏差及γ分析三维评价算法。 设计两个计划进行算法验证: 计划1为方野照射等效水, 用于验证算法的正确性; 计划2为适形野照射仿真头模, 用于验证算法的实用性。 结果表明, 计划1中, 对剂量偏差,容许值范围内通过率为100%; 对位置偏差和γ分析, 容许范围内通过率为100%,容许边界值处为100±7.7%。 计划2中, 3种算法通过率分别为88.35%、100%和95.07%。 这说明该算法可用于剂量引导精确放疗系统中实现三维剂量分布的评价。     

辐照三烷基氧化膦在水相中溶解度的研究

三烷基氧化膦是镧系元素和锕系元素的高效萃取剂。本文用ＩＣＰ－ＡＥＳ法测定萃余水相中的磷,用以研究三烷基氧化膦在纯水、酸液及碱液中的溶解度。结果表明,随着γ射线辐照剂量的增加,三烷基氧化水膦在水相中溶解度增加,并且在碱液中有较高的溶解度,在纯水中有较低的溶解度。     

碳离子束混合LET辐照的EBT3辐射变色胶片剂量修正方法

针对EBT3辐射变色胶片对碳离子束混合LET辐照的剂量欠响应比较了两种剂量修正方法。利用260MeV/u的碳离子束通过被动降能得到多种剂量平均LET的碳离子束,利用这些碳离子束进行了胶片剂量响应刻度辐照,选择最佳的拟合公式得到了胶片剂量刻度曲线。使用RE(Relative Efficiency)量化了EBT3胶片随LET的剂量欠响应,并使用RE剂量修正法修正了混合LET辐照胶片的剂量。此外,根据剂量刻度曲线公式中拟合参数随不同LET所占剂量比例的变化规律,提出了拟合参数剂量修正法并修正了混合LET辐照胶片的剂量。最后比较了这两种方法的结果,表明拟合参数方法得到的剂量偏差在5%以内,优于RE方法10%以内的剂量偏差。     

基于中国参考人体素模型环境外照射剂量转换系数的计算

基于中国参考人体素模型计算地面污染和空气浸没情况下环境外照射剂量转换系数,主要用于核事故情况下公众及工作人员有效剂量的快速估算.首先,采用二次源项方法,基于Geant4模拟进入人体周围圆柱面入射光子的高度、角度和能量分布;其次,利用中国参考人体素模型和二次源项结果作为MCNPX模拟的输入项,计算15 keV至10 MeV能量范围内20组单能光子外照射剂量转换系数,和文献数据吻合;最后,利用ICRP第107报告核素衰变程序并对单能光子外照射剂量转换系数进行插值,计算了核事故情况下68种常见核素外照射剂量转换系数.与本文结果对比,国标中用于快速估算人员受照剂量转换系数值在地表沉积情况下偏保守,而空气浸没下中高Z放射性核素则偏低.     

聚四氟乙烯的辐射效应及其ESR研究

该文回顾了从上世纪50年代中期至近年来人们在聚四氟乙烯（PTFE）辐射效应方面的研究工作,初步总结了辐射PTFE产生的自由基及其相应的过氧化自由基的电子自旋共振（ESR）波谱学应用研究,总结并讨论了实验温度、辐射剂量、PTFE粉末形式、结晶度和交联等因素对辐射PTFE自由基ESR信号的影响. 同时还简要介绍了辐射PTFE后的自由基反应以及辐射交联的进展情况.     

Electron Spin Resonance (ESR) Dating of Calcareous Fault Gouge of the Ushikubi Fault, Central Japan

The ages of fault events of active faults have been estimated using electron spin resonance (ESR) signals of siliceous gouges. This technique of ESR method is limited by obtaining only ages that are greater than tens of millennia. So this study focuses on developing a new technique of using calcareous gouges to gain an insight into the ages of latest seismogenic event within the Holocene. For the first time, signal B of the ESR method has been used to estimate the age of the Ushikubi fault from calcareous gouge. This technique proved reliable because the mean age (1.9 ka) obtained agrees with previous works on indirect age determination of latest fault events by utilizing radiocarbon dating in the study area. However, the result from the ESR technique showed an increase relative to the age of 1 ka that was obtained by the radiocarbon dating method. This disparity may be due to a high dose rate value of 50 Gy/h of artificial irradiation that was used to determine the equivalent dose (ED). Moreover, isochronal experiment revealed that the gouge did not comprise pure carbonates but consisted of a mixture of calcite and quartz grains. A younger age value would have been obtained if a lower artificial irradiation dose rate and a relatively pure carbonate fault gouge were used in the ED determination.     

Testing the reliability of ESR dating of optically exposed buried quartz sediments

Optical dating of quartz by optically stimulated luminescence has a time range that is generally less than about 500 ka, due to relatively rapid saturation of the available luminescence defects in quartz. We test here a new method, electron spin resonance (ESR) optical dating of quartz, in which radiation-sensitive defects at aluminum and titanium atoms on silicon sites give rise to signals which can only be detected near liquid nitrogen temperature and which have a much higher capacity to absorb radiation dose before saturating than optical luminescence-detected signals. Our results show this method yields agreement with independent age control out to about 2.5 million years, extending here the dating range of optically exposed quartz in sediments in along-shore sediments (aeolian and waterlain) by a factor of about 5. Three sites in along-shore lacustrine and marine aeolian environments yielded very good agreement with independent age control. Details of single saturating exponential fitting in relation to agreement with expected burial doses and annealing of Al and Ti signals provide additional data to consider the best approaches to the dating method. Furthermore, we propose a new criterion for ESR optical dating: both the Al signal and Ti signal ages must agree to insure accurate burial ages. Moreover, when Al signal ages are lower than Ti signal ages, then the Al signal may be taken as the minimum burial age.     

Experimental determinations of beta attenuation in planar dose geometry and application to ESR dating of tooth enamel

Two experiments were performed to determine the distribution of beta dose in a target medium as a function of distance from a planar source (2π geometry). In Experiment 1 planar absorbers were used to simulate depth in the target medium, and the attenuated dose that penetrated the intervening absorbers was detected using thermoluminescence from CaSO₄:Tm. In experiment 2 pellets of powdered tooth enamel were situated in a cavity in solid tooth enamel. Dose response of the electron spin resonance (ESR) signals in the pellets allowed direct detection of dose distribution within the target medium. The dose distributions were found to agree more closely with Monte Carlo calculations and with one-group transport theory (Prestwich et al., 1997 and Brennan et al., 1997) than with approximations used widely in ESR dating applications (Grün, 1986). Although the latter were supported by experiments by Aitken et al. (1985), the results of experiment 1 provided data to suggest that departure from 2π geometry was unacceptably large in the Aitken et al. (1985) configuration. The beta doses obtained by one-group theory in typical target volumes of enamel were 17 to 40% lower than those obtained using the Grün approximation. It was concluded that one-group transport theory provides the best available routine tool for calculations of beta dose attenuation in near-planar target materials (e.g. tooth enamel and shell) irradiated by natural sources, although Monte Carlo methods are better and could eventually be introduced into the ROSY ESR dating program (Brennan et al., 1997). It was also concluded that a revision of previously published ESR ages using one-group transport for beta dosimetry will be needed. For cases where the U concentrations in enamel are generally low (less than a few ppm), previously published ESR ages on tooth enamel are systematically too young by 5–30%.     

Alpha and beta dose gradients in tooth enamel

New results describing gradients in effective alpha and beta doses within a layer of tooth enamel in planar geometry are presented. The alpha (track) dose to an enamel layer is calculated using an algorithm similar to that of Aitken (Aitken, M.J., 1987. Alpha dose to a thin layer. Ancient TL 5, 1–3.). The code for ROSY version 1.4 (Brennan, B.J., Rink, W.J., Rule, E.M., Schwarcz, H.P., Prestwich, W.V., 1999. The ROSY ESR dating software. Ancient TL, in press.) incorporates this algorithm. The approach allows for variation of the alpha track dose near the edges of the enamel, and we describe the gradient of the alpha track dose within 40 μm of each edge of the enamel for natural sources. In ESR or luminescence dating of naturally thin layers, for which stripping of the surface layer containing the alpha dose gradients may not be feasible, age estimates may change by as much as 5–10% when the detailed alpha dose calculation is included. Modern Monte Carlo-based results for the variation of beta dose for depths up to 2 mm are compared with ROSY results. For external irradiation by different sources, the attenuation of the ROSY dose estimate with depth is usually less rapid than that of the Monte Carlo-based estimate. The ROSY estimate of average beta dose to a layer in this case is between 5 and 18% higher than the Monte Carlo estimate.     

Concepts and methods of ESR dating

Electron spin resonance (ESR) dating is an absolute dating method suitable for the Quaternary which can be applied to a wide range of materials. It is based on determining the natural radiation dose to which a sample has been exposed during its burial period. This paper outlines the basic concepts, and reviews recent studies on the methods and models of ESR dating.

Scope of this paper. This review paper is one of two in this volume providing an overview of recent developments in the field of electron spin resonance (ESR) dating. The paper focuses on studies investigating the fundamental concepts and methods employed in ESR dating, while the companion paper by Rink (this issue) focuses on applications of the method. Previous review articles have been published by Ikeya (1978) and Ikeya (1985), Hennig and Grün (1983), Nambi (1985) and Grün (1989b). Subsequently, papers by Grün (1991), Schwarcz (1994) and Ikeya (1994a); Ikeya (1994b) and Ikeya (1994c) have reviewed specific aspects of the field. There are three books on ESR dating by Ikeya (1986), in Japanese), Grün (1989a)Grün (1989b), in German) and Ikeya (1993), in English) respectively. In view of the coverage of previous reviews of the field, this paper concentrates on research undertaken since 1990.

The first part introduces and outlines the basic ideas of ESR and its application to dating. This is followed by an overview of recent studies concerned with the basic concepts of the field, its methods and models, as independently of specific materials as possible.     

Model correction for the formation of amorphous silicon by ion implantation

The critical dose at which an implanted amorphous layer in silicon is formed cannot be explained by a previous energy independent model. An energy dependent correction to this model can explain our ESR data as well as other data. The correction is most important for light ions.     

Composition,temperature and radiation induced changes in gamma irradiated AAAMPS copolymer

Effect of composition, temperature and radiation dose in gamma irradiated acrylamide-2-acrylamido-2-methyl propane sulphonic acid (AA) copolymer has been investigated by electron spin resonance (ESR) and fourier transform infrared (FTIR) techniques. ESR spectra of gamma irradiated AA copolymer have been recorded under different conditions. The observed ESR spectra are analysed by computer simulation techniques, to separate the constituent component spectra. Magnetic parameters employed to simulate the component spectra enabled the identification of corresponding free radicals. The AA copolymer with low acrylamide content composed of macroradicals of the type ?CH₂?CH?CH₂? and methyl radicals (CH₃) whereas the copolymer with high acryl amide content possess methyl radicals and radicals of the type ?CH₂?C(CONH₂)?CH₂?/CH₃?C?CH₃. Reasons for the variation in the formation of free radicals have been explained. The observed changes in ESR spectra of irradiated AA copolymer at higher temperatures are thought to be due to the recombination of free radicals. Formation of free radicals found to be enhanced with the increase in dose of irradiation. FTIR spectra of pure and irradiated copolymers have also confirmed the previous results.